Adhesives are generally applied as a liquid that eventually solidifies and binds to a surface. From ancient times, water based adhesives (glues) were extracted from plant or animal sources. These glues usually bound to surfaces, or bound two surfaces together, as they slowly dried. With the advent of plastics and other modern polymers, adhesives were created that solidify and bind surfaces through chain elongation chemistries (polymerization). Still, adhesives have tended to be applied and cured in an imprecise and wasteful manner.
Glues and adhesives can be applied to surfaces with some precision or generally smeared about the work piece. Adhesives can be applied imprecisely by brushing, dipping, pouring, and spraying if the adhesive is inexpensive and if excess can drain aside without harm. Where excess adhesive can damage the work piece, skilled application (e.g., intricate brush work) or high technology provides techniques for more precise application.
Flow dams can be established to limit the flow of adhesives. In U.S. Pat. No. 5,409,863, entitled “Method and Apparatus for Controlling Adhesive Spreading when Attaching an Integrated Circuit Die”, for example, a solder mask ring barrier is screen printed around the periphery of a die mounting pad of an integrated circuit to prevent adhesive flow onto surrounding circuit electrical contacts. In another example, U.S. Pat. No. 6,084,311, entitled “Method and Apparatus for Reducing Resin Bleed During the Formation of a Semiconductor Device”, the flow of adhesive is constrained within a low surface tension area by a surrounding high surface tension dam. The mounting position of a semiconductor chip on an electronic lead frame pad is covered with a low surface tension composition attractive to an adhesive, but surrounded with a high surface tension composition repellant to the adhesive. When the chip is mounted to the pad, the adhesive flows between the semiconductor and low surface tension region but tends not to flow onto the a high surface tension region or surrounding circuitry. In these technologies, precise adhesive application requires precise pre-application of the dam compositions.
Polymers can be precisely located by light directed polymerization (curing) of resins. For example, in U.S. Pat. No. 6,139,661, entitled “Two Step SMT Using Masked Cure”, terminals of an integrated circuit are generally coated with an unpolymerized electrical conductive adhesive. Test electrode leads are temporarily bonded to specific terminals by placing the test lead into adhesive on the terminal followed by spot illumination of the terminal, through a mask. Adhesive at the test terminal is polymerized while adhesive at other terminals remains unpolymerized and available for later testing. Such spot curing techniques can provide precise bonding of adhesive but requires adhesives to be previously applied at the site. These spot curing techniques are not intended to prevent adhesives from migrating onto restricted surfaces. Adhesive applied, but not spot cured, remain as a wasteful messy residue.
A need remains for methods and equipment to precisely situate polymers without leaving residue on adjacent surfaces, or having to preprint dam boundaries. Spot curing methods that could precisely direct polymerization can benefit from techniques that do not require pre-application of the adhesive and exclude adhesive from surfaces sensitive to adhesive residues. The present invention provides these and other features that will become apparent upon review of the following.